gr - q c / 97 06 03 0 1 1 Ju n 19 97 1 Black Hole Entropy : a spacetime foam approach

I introduce the spacetime foam structure by reviewing briefly the ideas of Wheeler, the topological fluctuations and the virtual black holes possibility. The contribution of Jacobson (the equation of state of the foam) is recalled. In the second part, I introduce a model of spacetime foam at the surface of the event horizon of a black hole. I apply these ideas to the calculus of the number of states of a black hole, of its entropy and of other thermodynamical properties. A formula for the number of microholes on the surface of the event horizon is derived. Subsequently, I extend the thermodynamical properties of the event horizon to thermodynamical properties of the space. Here I face with the problem of the maximum entropy contained in a space region of a given volume. In the end, on the basis of the results previously obtained, I briefly treat the possibility of micro black holes creation by Unruh Effect.